As an example of mobile communication systems, in recent years, the Institute of Electrical and Electronics Engineers (IEEE) works toward the standardization of wireless communication systems called Worldwide Interoperability for Microwave Access (WiMAX). WiMAX has two standards. One is IEEE 802.16d for fixed subscriber stations, and the other is IEEE 802.16e for mobile subscriber stations (hereinafter, “mobile stations”). The standardization of IEEE 802.16m, which is the next generation of IEEE 802.16e, is also in progress.
Mobile stations based on IEEE 802.16e or the like perform wireless communication with a macro base station operating in a wired network called an access service network (ASN). The macro base station performs wireless communication with mobile stations within a range (hereinafter, “macro cell”) where radio waves transmitted from the macro base station are received. Various methods for detecting the position of a mobile station have been studied for a wireless communication system in which wired base stations such as macro base stations operate. Specifically, for example, the position of the mobile station can be detected based on transmission delays and the power loss of signals transmitted between the base station and the mobile station. According to the methods, a mobile station performs signal transmission/reception with a plurality of base stations, and the position of the mobile station is calculated based on, for example, the coordinates of each of the base stations and transmission delays of signals. Published Japanese Translation of PCT Application No. 2003-520532 and Japanese Laid-open Patent Publication No. 2004-301850 disclose technologies for measuring the radio wave environment between the mobile station and the base stations, and calculating the position of the mobile station based on the measurement result.
The IEEE 802.16e defines that a macro base station broadcasts a message (MOB_NBR-ADV: mobile neighbor advertisement) that includes information on adjacent macro base stations. Accordingly, the mobile station may receive the message from the macro base station to determine one or more macro base stations to/from which signals can be transmitted/received. The first macro base station, which is in communication with the mobile station, and the other macro base station which is adjacent to the first macro base station may perform signal transmission/reception with the mobile station to detect the position of the mobile station.
A macro base station is generally large and installed outdoors, and a macro cell is also relatively large. Accordingly, if the macro base station is installed, wireless communication can be performed in a relatively wide range. However, sufficient communication quality cannot be obtained inside a building and the like where radio waves are hard to reach.
Accordingly, in the WiMAX, an introduction of a femto base station that is smaller than the macro base station has been investigated. The femto base station is mainly installed inside a building such as a house, and although a range (hereinafter, “femto cell”) in which transmitted radio waves can reach is relatively narrow, it is possible to provide wireless communication service to mobile stations.
As described earlier, the macro base station broadcasts information related to adjacent macro base stations. The broadcasted information (hereinafter, “adjacent-station information”), however, does not include information on femto base stations. Accordingly, the mobile station cannot easily identify a femto base station to/from which signals can be transmitted/received. Consequently, it is difficult to use a femto base station to detect the position of the mobile station.